The overall objectives of the proposed research are 1. to quantify carbohydrate absorption in cystic fibrosis (CF); 2. to determine the effect of chronic oral antibiotic therapy on intestinal bacterial metabolism of malabsorbed dietary and endogenous carbohydrates and carbohydrates in glycoproteins; 3. to determine whether small bowel bacterial overgrowth is present in CF. The proposed approach takes advantage of the noninvasive, highly specific and sensitive techniques of breath analysis as well as in vitro fecal incubations previously shown to model in vivo colonic bacterial metabolism of carbohydrates. Excretion of H2 in breath will indicate the quantity of carbohydrate escaping small bowel absorption. The results obtained in vivo using breath measurements will be correlated with data in vitro obtained using measurements of bacterial metabolism of test substrates. Correlation of expired air and in vitro measurements will indicate any therapy-induced shifts in fermentation by the enteric bacterial ecosystem. Thus, variables affecting H2 production in vivo which are independent of absorptive capacity for a given sugar will be recognized. In addition, the fecal incubation system will permit investigation of intestinal bacterial metabolism of non-dietary endogenous glycoprotein substrates in CF. The carbohydrate portion of nutrient intake is of special importance in provision of energy to the CF patient, since loss of calories in the form of other macronutrients, principally fat, may be extensive. The present proposal should provide quantitative information acquired noninvasively on digestion and absorption of sugars in individuals with CF, and the data obtained should be directly applicable to dietary and pharmacologic management in these patients. Similarly, the proposed studies utilizing endogenous glycoproteins may provide important insights into the role of enteric bacteria in degradation of mucins accumulating in CF intestine.